The invention relates to a method for operating a preventive-action protection system in a motor vehicle which has safety devices for mitigating the consequences of accidents.
Protection systems which act in a preventive fashion even before a possible collision and use what is referred to as a pre-crash phase (i.e., a period of time starting from the detection of a high probability of a collision by appropriate detection systems in the vehicle up to the actual impact) to enhance the vehicle occupant protection by means of additional safety measures and thus lessen the severity of an accident, are referred to as preventive-action protection systems or so-called PRE-SAFE™ systems. In order to detect possible accident situations, preventive-action protection systems use information which from various sensor devices of the motor vehicle. The sensor devices here may also be a component of an electronic driving stability program or an inter-vehicle distance sensor system. Depending on the detected situation, conclusions are drawn about a possible accident, and appropriate measures, relating to restraint systems for vehicle occupants and possibly protection devices for other parties in an accident (such as pedestrians) are initiated in order to condition the vehicle for the imminent accident.
In such a method for actuating a reversible vehicle occupant protection means in a motor vehicle, as is disclosed, for example in German patent document DE 101 21 386 C1, the motor vehicle has a reversible vehicle occupant protection system which can be activated before a collision, and thus moved into an effective position. For this purpose, a sensor system is used to acquire driving state data which is monitored for any possible emergency braking, any possible oversteering and any possible understeering. If emergency braking, oversteering and/or understeering are detected, the vehicle occupant protection system is activated, and further conditions may be provided for the triggering operations. The sensor system for acquiring the driving state data may be a steering angle sensor, a pedal travel sensor, a brake pressure sensor, a wheel speed sensor, an acceleration sensor and a yaw rate sensor.
An emergency braking operation occurs if a braking process takes place with at least one feature which indicates a hazard situation or emergency situation. The state of emergency braking is determined by using at least one of the parameters of brake pressure, speed of the activation of the brake pedal and speed of the withdrawal of pressure from the accelerator pedal to evaluate the braking process. As an alternative to emergency braking which is brought about by the driver (driver reaction) it is possible to bring about emergency braking based on sensing of the surroundings.
As disclosed in German patent document DE 101 21 386 C1, the state of emergency braking can be detected by means of an intervention by a brake assistance system in the vehicle movement dynamics. For example, an information signal which is transmitted from the brake assistance system to a data bus may be used to detect the state of emergency braking. Triggering of the safety devices of the protection system is then coupled to the algorithm of the brake assistance system. The signal of the brake light switch which is also made available on the data bus of the vehicle can also be used to confirm (check the plausibility of) the detection of the state of emergency braking. With this redundancy in the detection of an emergency braking operation, the reliability of a decision when the protection system is triggered is increased.
A further preventive-action protection system is disclosed in German patent document DE 100 29 061 A1. In order to detect a state of emergency braking, the time gradient (that is time derivative) of the brake pressure which is generated by the brake pedal is evaluated. The fact that a threshold value is exceeded by the brake pressure gradient is indicative of an emergency braking state. The pedal travel or the pedal force can also be measured as a representative of the measured brake pressure. In order to check the plausibility of the decision, the brake pressure is also submitted to evaluation in parallel to the brake pressure gradient, by comparing the brake pressure with a brake pressure threshold value and comparing the time when the threshold was exceeded by the measured brake pressure with a predefined time period. This is intended to separate out brief braking situations in which the brake pressure gradient is above the brake pressure gradient threshold but the braking request is not present for long enough with an intensity above the threshold.
In addition according to German patent document DE 100 29 061 A1, the longitudinal deceleration (longitudinal braking measured value) of the vehicle and the state of an anti-lock braking system (ABS) may also be monitored in a separate decision channel with regard to the presence of an anti-wheel lock system. A potential accident situation is determined if the longitudinal deceleration exceeds a threshold value during a specific time period in the course of the brake slip control operation.
One object of the invention is to provide an improved method for a preventive-action protection system of the type specified in the introduction.
This and other objects and advantages are achieved by the methods according to the invention, which make it possible to react better to real driving states in that the triggering of the safety devices is also made dependent on the fact that the longitudinal deceleration of the vehicle which is caused by the braking intervention is not yet far advanced. In this method, triggering of the safety device is suppressed as soon as the braking intervention results in a perceptible longitudinal deceleration which, on the one hand, indicates that the vehicle is reacting sufficiently to a braking torque request by the driver (controlled braking) and on the other hand prevents pretensioning of a seatbelt (which is no longer appropriate) when the longitudinal deceleration and forward movement of the vehicle occupant have already occurred. At this time, the forward movement of the vehicle occupant would in fact have already advanced so far that it could no longer be reversed in sufficient time before the impact by the pretensioning.
The interrogation of the longitudinal deceleration permits triggering scenarios for an extended spectrum of driving situations which are critical in terms of longitudinal dynamics to be provided. It is also possible to assign such braking situations to the state of emergency braking which indicate a hazard situation or emergency situation but have until now not been sufficiently taken into account by the known methods: if the driver however depresses the brake pedal slowly but very strongly, a high degree of criticality also occurs if the vehicle does not react correspondingly to the braking torque request (panic braking), either because the brakes fail or because the tires are not adhering sufficiently to the underlying surface (that is, the coefficient of friction is low). This relates in particular to emergency-like braking processes on a slippery underlying surface (for example due to snow, ice, coverage with foliage) or in the case of aquaplaning. Such braking processes are not detected as critical by the known methods which link the detection of the state of emergency braking to the brake pedal activation speed, the gradient of the brake pressure or to the braking assistant.
In one advantageous embodiment of the invention, a state of emergency braking is determined if the braking torque request exceeds a request threshold. However, safety devices are activated only if at the same time the longitudinal deceleration of the vehicle does not exceed a threshold.
In addition or as an alternative, the braking torque request speed is observed with respect to the exceeding of a threshold, in order to detect the requesting of an emergency braking operation. In one advantageous embodiment this threshold can be controlled as a function of the brake pressure request. Since the request speed threshold decreases as the braking request increases, sudden activation of the brake pedal subsequent to a normal braking operation can be detected as an emergency braking operation even though the available activation travel is reduced.
The thresholds for the braking torque request or the braking torque request speed can be influenced by the driving state data. In particular, at low driving speeds (below approximately 30 km/h) the thresholds can be raised so that incorrect triggerings or undesired triggering in this speed range can be effectively suppressed. At speeds above approximately 80 km/h, the thresholds can be lowered because at higher speeds the driver has been empirically found to depress the brake more sensitively. It is also conceivable to influence the threshold as a function of the transverse acceleration. In particular, the thresholds could be lowered in a central transverse acceleration range.
In many cases, the signal for the braking request speed is formed by deriving the braking request signal over time. As is explained below, it may, however, be advantageous for the formation of the braking request speed and braking request signal to make use of different measurement variables which represent the braking torque request of the driver.
Basically, the brake pressure in the master brake cylinder can be used as an underlying measurement variable to acquire the braking torque request and to detect an emergency braking request by the driver. However, the brake pressure in the master brake cylinder reacts very slowly to a sudden braking torque request by the driver and is therefore less suitable for sensing rapid changes in the driver's requests.
In a conventional hydraulic system, a diaphragm travel sensor senses both the pedal movement and the diaphragm movement of the brake booster. The diaphragm travel sensor thus reacts much more directly to the pedal travel than the brake pressure in the master brake cylinder. In an electrohydraulic brake system (brake-by-wire system) a pedal travel sensor picks up the activation of the brake pedal directly. If a diaphragm travel sensor or pedal travel sensor is present, it is therefore alternatively or additionally also possible to use such sensor to sense the braking torque request.
According to one advantageous refinement of the invention, the signal of a pedal travel or diaphragm travel sensor is used to obtain the braking torque request speed from the derivative of the signal over time. Using these measurement variables has the advantage that the pedal travel initially represents the driver's request without disruption and directly, because of a delayed reaction of the back pressure in the brake system on the activation of the brake, the pedal does not yet have to be depressed against a high resistance. A reaction of the brake system against the pedal force does not occur until later in the course of the activation. The signal of a pedal travel sensor or diaphragm travel sensor is also possibly unusable during an ABS controlled intervention due to the pulsating reaction on the brake pedal. In particular, pedal travel measurement or diaphragm travel measurement is therefore suitable for early sensing of a rapid braking torque request by the driver.
However, the pressure in the master brake cylinder is a highly suitable variable for evaluating a slow and enduring braking torque request because said pressure follows the activation of the brake pedal with a certain degree of inertia. As a result many brief braking situations can already be separated out because a sufficient brake pressure is not generated.
Accordingly, an advantageous combination is one in which the evaluation of slow and enduring braking torque requests is supported on the brake pressure in the master brake pressure cylinder, while the braking torque request speed is acquired from the time derivative of a signal of the pedal travel sensor or diaphragm travel sensor.
If there is a reproducible relationship between the pedal travel and a pedal restoring force, a pedal force sensor can be used instead of a pedal travel sensor. However, if the restoring force of the brake pedal is due to a reaction of the backpressure in the brake system, the relationship is no longer unambiguous. In this case, the pedal force corresponds more to the brake pressure in the master brake cylinder.
In addition to the known safety devices which can be triggered in a preventive fashion, such as the reversible seat belt pretensioner of a seat belt, there are a series of further vehicle occupant protection means which can be actuated and which produce a restraining effect or an energy-absorbing effect in order to protect a vehicle occupant in the event of a collision. Examples of such vehicle occupant protection means are movable impact elements, cushions and headrests whose size, hardness, shape and position can be changed by means of an actuation process. In addition to these vehicle occupant protection means, further safety devices which can be actuated can be provided for reducing the severity of an accident. Such safety devices reduce the consequences of an accident for a vehicle occupant by actuating electrically adjustable assemblies, for example an electric seat adjustment device or an electric adjustment device for vehicle openings (window lifter, sunroof closing system) or door locks, which were originally provided for comfort purposes.
In order to diminish the consequences of accidents, it is also possible to provide safety devices which can be actuated in motor vehicles and which also serve to protect other parties in a collision, in particular pedestrians and cyclists. Examples include adjustable engine hoods, movable bumpers and impact elements with adjustable hardness on the outer skin of the vehicle. Further protection means which can be actuated are the ride level controller and the braking and steering system by which an impact can be optimized in the direction of less severe injury to the vehicle occupants and/or the parties in a collision. These protection means are also to be understood below as safety devices within the sense of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.